There is no point in playing Portal 2 unless you’ve played Portal 1. It’s not that you couldn’t play the game, it’s just that I think that this is not the sort of game that is going to be as easy to appreciate without experiencing the first episode.
The length of the game felt good; some may say it’s a little brief for the full price tag, but I felt like I got my money’s worth in the single player campaign. The puzzles weren’t too difficult in general; there were only a few in the middle that got a bit trying. The story was actually a story, of sorts, and the effort put into decorations and the overal visual aesthetic of the game are downright impressive.
Anyway, don’t play it unless you’ve played the first one, but play both. 9/10.